This invention relates to a sheet feeder mounted in a printer for feeding cut sheets for printing one by one to a printing position of the printer.
In a prior art sheet feeder of the pertaining type, a plurality of, e.g., two sheet holder sections are provided for holding respective stacks of printing sheets of different sizes. Feed roller pairs are each provided for each of these sheet holder sections such that they can be selectively rotated to feed sheets from a corresponding sheet holder section
In such a prior art sheet feeder, however, a drive motor is provided in each sheet holder section to drive each feed roller pair. This means that an independent mechanism for coupling drive torque is provided from each motor to the associated sheet holder section. This arrangement complicates and increases the size of the construction of the sheet feeder, thus increasing the cost of manufacture.
There is a sheet feeder which uses a common drive motor for a plurality of sheet holder sections. In this case, solenoid units are provided such that they are selectively operable to select corresponding sheet holder sections. This sheet feeder, therefore, has a complicated electric circuit for solenoid unit selection control, thus presenting problems like those noted above.
The prior art sheet feeders as described above are disclosed in United States patent specification Nos. 4,564,187, 4,577,849, 4,645,192, 4,664,546 and 4,667,947.
A prior art sheet feeder comprises opposite side sheet support members for supporting the opposite sides of a stack of sheets and an intermediate sheet support member provided between the opposite side sheet support members for supporting the back of the sheet stack, these members being supported with respect to the sheet feeder frame for displacement in the width direction of the sheet so that the sheet feeder will comply with a change in the width size of the printing sheet.
In the prior art sheet feeder, however, the intermediate sheet support member that is provided between the opposite side sheet support members is mounted on the sheet feeder frame such that it can not be removed. Therefore, it is difficult to hold a stack of narrow printing sheets, e.g., postal cards, which are extremely different from normal size sheets by making use of the sheet support members. This is so because the intermediate sheet support member is considerably wide so that it interferes with the displacement of the opposite side sheet supports to positions close to each other, that is, the opposite side sheet supports can not be brought to close-to-each-other positions complying with the size of the narrow printing sheet, such as a postal card. The feed rollers also can not be in contact with the printing sheet, so that the printing sheet can not be fed.
In order to be able to bring the opposite side sheet support members to the close-to-each-other positions complying with a narrow printing sheet, an intermediate sheet support member having a reduced width has to be used. However, a narrow intermediate sheet support member is liable to be readily deformed by the weight of the supported sheet stack so that it can not sufficiently support the back of the sheet stack.